The principles of the silver complex diffusion transfer reversal process, hereinafter called DTR-process, have been described e.g. in U.S. Pat. No. 2,352,014 and in the book "Photographic Silver Halide Diffusion Processes" by Andre Rott and Edith Weyde--The Focal Press--London and New York, (1972).
In the DTR-process non-developed silver halide of an informationwise exposed photographic silver halide emulsion layer material is transformed with a so-called silver halide solvent into soluble silver complex compounds which are allowed to diffuse into an image receiving element and are reduced therein with a developing agent, generally in the presence of physical development nuclei, to form a silver image having reversed image density values with respect to the black silver image obtained in the exposed areas of the photographic material.
A DTR-image bearing material can be used as a planographic printing plate wherein the DTR-silver image areas form the water-repellant ink-receptive areas on a water-receptive ink-repellant background.
The DTR-image can be formed in the image receiving layer of a sheet or web material which is a separate element with respect to the photographic silver halide emulsion material (a so-called two-sheet DTR element) or in the image receiving layer of a so-called single-support-element, also called mono-sheet element, which contains at least one photographic silver halide emulsion layer integral with an image receiving layer in waterpermeable relationship therewith. It is the latter mono-sheet version which is preferred for the preparation of offset printing plates by the DTR method.
Two types of the mono-sheet DTR offset imaging elements exist. According to a first type disclosed in e.g. U.S. Pat. No. 4,722,535 and GB- 1,241,661 a support is provided in the order given with a silver halide emulsion layer and a layer containing physical development nuclei serving as the image-receiving layer. After informationwise exposure and development, the imaged element is used as a printing plate without the removal of the emulsion layer.
According to a second type of mono-sheet DTR offset imaging element a hydrophilic support, mostly anodized aluminium, is provided in the order given with a layer of physical development nuclei and a silver halide emulsion layer. After informationwise exposure and development, the imaged element is washed with water to remove the emulsion layer so that a support carrying a silver image is left wich is used as a printing plate. Such type of lithographic printing plate is disclosed e.g. in U.S. Pat. No. 3,511,656.
EP-A-410500 discloses an imaging element containing a support provided with an image receiving layer and a silver halide emulsion. In said document is disclosed a diffusion transfer reversal process for obtaining a lithographic printing plate in which said imaging element is imagewise exposed and subsequently developed using a developing liquid or activating liquid in the presence of a silver halide complexing agent. The imaging elemnt is then guided through a diffusion transfer zone so that the silver halide complexes formed during the development step are allowed to diffuse into the image receiving layer where they are converted to silver. When the imaging element leaves the diffusion transfer zone a silver image is formed in the image receiving layer. Hereafter, the imaging element passes a washing and a rinsing station to remove the silver halide emulsion layer so that the silver image is exposed. Finally the imaging element, now carrying a silver image on its surface, is treated with a finishing liquid that contains a so called hydrophobizing agent for improving the hydrophobicity of the silver image.
However, said washing requires several precautions, as e.g. a gently or softly washing of the developed monosheet layer assemblage alone is not sufficient to remove the now superfluous emulsion layers from the imaging element, but a certain mechanical force is required.
Therefor, sometimes brushes, sponges, scrapers or squeegee blades, wiping or scrubbing rollers, etc are applied--either individually or separately, or in combination together-, but these elements can damage the image, especially in case of high resolution images.
According to the state of the art relating to the present invention, several attempts have been made of using a spray in a washing station of a processing apparatus.
U.S. Pat. No. 3,589,261 applies in a washing station at the entrance a first spray which gives a hard scrubbing action to the surface of the element and at its exit a second spray which gives a light rinsing action to the element.
In U.S. Pat. No. 4,142,194 a rinsing section comprises water impact sprays and barrier means (e.g. a wiper) extending longitudinally of the upper drive roller.
The apparatus "Silverlith", e.g. processor SLT, marketed by Du Pont, comprises a washing section and a rinsing section. In the washing section warm water is dripping out of a tube, without any substantial pressure, on an upper drive roller, which is a scrub roller, as well as on the element. In the rinsing section, water is sprayed on the element which is passed below a squeegee set to remove the water of the element.
The use of common sprays or jets tends to damage the image on the imaging element, or tends to cause clogging of pumps, valves and filters by fragments of the layers removed from the imaging element after its development, both phenomena being detrimental to image quality.